1. Field of the Invention
The present invention relates to a technology with respect to a detection method and a detection apparatus for obtaining information about a substance (sample) using an electromagnetic wave (referred to as a “terahertz wave”, or “THz wave”, herein) selected from a frequency range of 0.1 THz to 10 THz.
2. Description of the Related Art
In recent years, technologies using THz waves have actively progressed. In particular, the photon energies of THz waves are almost the same in level as those of skeletal vibrations of molecules and molecular interactions. Thus, spectra obtained by spectroscopic technologies have been used for the analysis of substances.
For such technologies, Japanese Patent Application Laid-Open No. 2005-172775 discloses a detection method for identifying a substance in a food product by irradiating THz waves having frequencies equal to characteristic vibration frequencies corresponding to the structures of constituting elements of food products including DNAs, proteins, bacteria, and viruses. The above patent document describes that differences among them with respect to their structures, the presence or absence of denaturation, the presence or absence of toxins, and the like can be quickly and simply determined.
Since the THz waves have vibration frequencies specific to respective substances, thus, it is generally known that the presence of any substance and its state can be recognized from the spectrum information of the THz waves.
However, polymeric materials and hydrates include many materials that present difficulties in discrimination of characteristic vibration spectra in the THz wave region. Thus, the above method has not always been capable of identifying substances, for the following reason: polymers have an infinite number of characteristic frequencies at the frequency band of THz waves, so, as a result of superposition, it is difficult to separate and observe a characteristic peak. In addition, the characteristic frequencies resulting from intermolecular forces may disappear as the molecules may enter an amorphous, solution, or hydrated state. In this case, a conventional method, such as infrared spectroscopy, can be used. Known types of infrared spectroscopy includes Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy. Spectrum data with respect to the binding of molecules with energy higher than THz waves has been stored in a database, so any substance can be simply evaluated.
In the case of protein analysis, for example, the ELISA method (Immunochemistry, vol. 8, pp. 871-874, Pergamon Press, 1971) and the Western Blotting method (Analytical Biochemistry, vol. 112, pp. 195-203, 1981) have been known as methods using antigen-antibody reactions. Those methods permit high-sensitivity measurements. Further, other methods using electromagnetic waves such as X-rays and light, magnetism, and ultrasonic waves are known for observing a state change inside a substance and a denatured state as a broad sense by measuring the crystal structure, phase transition phenomenon, phonon, collision relaxation phenomenon, and the like.